Chemistry and green construction

Green construction strives to make all steps of the construction process more efficient and environmentally benign. Cement, for example, is the most used construction material worldwide. The production of cement is very energy intensive and produces about 5% of all CO2 emitted [globally?]. By using alternative fuels and raw materials this figure can be reduced. Plastic waste and used tires are commonly used “fuels” in European cement kilns. Milling the cement clinker requires 50 kWh of electric energy per ton of cement. The addition of amines, polyalkylene glycols or polycarboxylate ethers (PCE) can reduce the required energy by up to ten percent.

Another big area for energy savings is asphalt, which has over 90% market share in road pavement. Most asphalt pavement is made and applied using the “hot-mix” process. In this process molten bitumen and aggregate is mixed at a temperature between 150 and 190 °C, transported and placed on-site keeping this temperature. This heating (and reheating when laying it) is very energy intensive. A “Warm mix” process, however, can reduce the temperature by 20 to 40°C, cutting energy input by about 30 percent. “Cold mix,” meanwhile, uses bitumen emulsions and works at ambient temperature. The energy required to produce “cold mix” totals about 5% of the energy required to produce “hot mix”. Emulsifiers, which produce stable emulsions, breaking when they come in contact with the aggregate, make this possible. The United States, France and

Brazil is the leading producer and user of of “cold mix." Various polymers (SBR, PE wax, PiB) can also be used to enhance the properties and longevity of asphalt regardless of the temperature used for paving. Those modifiers in combination with cold mix play a major role in the in-place recycling process for road repair, which is a very cost-efficient method of road repair. Most construction machinery use hydraulics, which lose a lot of energy to the internal friction and viscosity changes of the fluid. Adding viscosity modifiers makes it possible to reduce fuel consumption of construction machinery, while simultaneously enhancing productivity. Field tests showed as much as 5% fuel reduction, along with a 30% increase in productivity.

As these examples show - the chemical industry is contributing significantly to an increasingly “greener” construction process of which everyone profits directly or indirectly.

Stefan Mueller is a senior principal analyst with IHS Chemical. To learn more about developments in construction chemicals, including energy efficiency efforts, check out the specialty chemicals feature in this week's CW.